1. Field of the Invention
The present invention relates to a resin composition for molding comprising a polyamide resin, a thermoplastic polyester resin and a specified vinylic copolymer and having excellent mechanical properties and processability in molding.
2. Description of the Related Art
Although thermoplastic polyester resins are widely used as molding materials of virtue of their excellent mechanical properties, electrical properties and chemical resistance, low water absorbency and good processability, they have the problem of a low hydrolysis resistance, since a reduction in the strength thereof after exposure to hot water for a long period of time is serious. Although polyamide resins are also molding materials having excellent mechanical properties, electrical properties and chemical resistance like the thermoplastic polyester resins, they have the defect of a dimensional change and impairment of the mechanical properties due to water absorption by the amide group.
Various attempts were made at using a resin composition prepared by melt-blending a polyamide resin with a thermoplastic polyester resin for the purpose of making the best use of the excellent properties of these resins. However, when the resins of different kinds are melt-blended, the mutual dispersibility of them is usually low and the obtained mixture has only low mechanical strength and flexibility. Such attempts thus did not yield results of practical use. Although it is proposed in, for example, Japanese Patent Publication-A Nos. 103191/1976 and 42545/1983 to mix the resins in the polymerization step in order to overcome this defect, this proposal is also impractical, since a large-scale apparatus and a long mixing time are necessitated.
Further a composition comprising a mixture of a polyamide resin and a thermoplastic polyester resin, and incorporated therein, a reinforcing material or a compound effective in improving the impact resistance is proposed in, for example, Japanese Patent Publication-B Nos. 19101/1972 and 24465/1972, and Japanese Patent Publication-A Nos. 56742/1973, 34754/1981 and 49657/1982. Although the resin composition obtained by such a method has an improved mechanical strength and a water absorption rate lower than that of the polyamide resin, its tensile elongation at break is yet insufficient.